Spread spectrum communication system apparatus

ABSTRACT

A receiving apparatus eliminating the need for performing at all times a function provided for a mode that is most susceptible to deterioration in accuracy in adaptive modulation communication. In a spread spectrum communication system according to the present invention, a control unit reads a demodulating method from a control signal specifying the demodulating method, and on the basis of the read demodulating method, the control unit controls a sampling rate of an A/D conversion unit and a despreading unit, a number of pilot symbols used by a propagation path estimating unit, and a number of pilot symbols despread by the despreading unit. Thereby, when the demodulating method is other than 64-QAM, the sampling rate and the like adjusted to QPSK or 16-QAM can be set.

TECHNICAL FIELD

The present invention relates to a spread spectrum communication systemapparatus that controls receiver parameters of A/D conversion speed, apropagation path estimating method and the like.

BACKGROUND ART

An adaptive modulation and coding rate communication systemconventionally used changes a cording rate of error correction code anda degree of multi-value modulation according to propagation pathquality. Specifically, this system provides high-speed datacommunication for a user with a good propagation path quality whilesacrificing noise-resisting characteristics, and provides low-speed datacommunication for a user with a poor propagation path quality, attachingimportance to noise-resisting characteristics.

The communication system using such an adaptive modulation is used inradio communication systems such as GSM EDGE, HDR and the like. Also, asimilar system is expected to be used additionally in W-CDMA.

An example of the adaptive modulation and coding rate communicationsystem will be described with reference to Table 1 below.

TABLE 1 Mode Coding method Modulating method 0 R = 1/2 QPSK 1 R = 1/216-QAM 2 R = 3/4 16-QAM 3 R = 3/4 64-QAM

First, reception quality data indicating quality of received data istransmitted from a receiver to a base station. At the base station, thereception quality data is classified into four grades (modes 0 to 3).The mode 0 indicates the lowest quality, and the mode 3 indicates thehighest quality. The base station selects a coding method and amodulating method as shown in Table 1 on the basis of the mode of thereception quality data.

Table 1 shows two coding methods represented by R=½ and R=¾. The codingmethod represented by R=½ adds one redundant bit to one bit of inputdata. The coding method represented by R=¾ adds one redundant bit tothree bits of input data. Modulating methods include known QPSK, 16-QAM,and 64-QAM.

A relation of amounts of data transferred is expressed as follows:(R=½, QPSK)<(R=½, 16-QAM)<(R=¾, 16-QAM)<(R=¾, 64-QAM)

On the other hand, a relation of noise resisting characteristics isexpressed as follows:(R=½, QPSK)>(R=½, 16-QAM)>(R=¾, 16-QAM)>(R=¾, 64QAM)

Thus, the amounts of data transferred and the noise resistingcharacteristics have relations opposite to each other.

Hence, when a coding method and a modulating method are selected asshown in Table 1, the mode 0, indicating the lowest quality, allowscommunications with enhanced noise resisting characteristics. The mode3, indicating the highest quality, allows communications transferring alarge amount of data.

With the conventional technology as described above, reception qualitydata is transmitted from a receiver to a base station, and the basestation selects a combination of an optimum modulating method and codingmethod on the basis of the reception quality data. Thus, the receiver isrequired to maintain good reception characteristics in all combinationsof the modulating methods and coding methods handled by the basestation.

A comparison of the modulating methods QPSK, 16-QAM, and 64-QAMindicates that 64-QAM is more susceptible to a shift in receptiontiming, an error in synchronous detection and the like, as compared withthe other methods. FIG. 1 is a graph showing a comparison of effects ofshifts in reception timing on the modulating methods. As shown in FIG.1, 64-QAM is most susceptible to shifts in reception timing. FIG. 2 is agraph showing a comparison of effects of errors in synchronous detectionon the modulating methods. As shown in FIG. 2, 64-QAM is mostsusceptible to shifts in reception timing.

64-QAM and 16-QAM are susceptible to multipath interference specific toa mobile communication environment. Accordingly, when 64-QAM or 16-QAMis used, it is necessary, for efficient communication, to suppress theinterference by using an interference canceller and an equalizer.

Thus, a high-performance receiver compatible with the adaptivemodulation and coding rate communication system needs to be designed inaccordance with the mode (64-QAM in this case) in which accuracy of eachreceiving function is most likely to deteriorate due to a shift inreception timing and the like.

Such high performance, however, is not necessary at the time ofreception in a mode in which accuracy of the receiving function does notdeteriorate.

Also, highly accurate reception processing generally requires anincrease in speed of signal processing, and thus increases powerconsumption. A mobile terminal such as a portable telephone, of whichlow power consumption is required, needs to perform only a minimumfunction required for reception. Hence, there is a problem withoperation at all times of a functional block designed for the 64-QAMmode.

It is accordingly an object of the present invention to provide acommunication apparatus and the like that eliminate the need forperforming at all times the function provided for the mode in whichreception accuracy tends to deteriorate in the adaptive modulationcommunication.

DISCLOSURE OF INVENTION

The present invention relates to a despreading device. The despreadingdevice according to the present invention receives a spread signal to bereceived. The despreading device according to the present inventionincludes receiving means, despreading means, sampling rate supplyingmeans, and control means.

The receiving means receives a signal to be received that has a controlsignal specifying a demodulating method. The despreading means despreadsthe received signal on the basis of a sampling rate, and then outputsthe control signal. The sampling rate supplying means supplies thesampling rate to the despreading means. The control means controls thesampling rate on the basis of the control signal.

According to the invention comprised as described above, the controlmeans controls the sampling rate of the despreading means on the basisof the control signal specifying the demodulating method. Thereby thesampling rate can be set lower as appropriate according to thedemodulating method, and a function (high sampling rate) provided for ademodulating method that is most susceptible to deterioration inaccuracy may not be performed at all times.

The present invention also relates to a propagation path estimatingdevice. The propagation path estimating device according to the presentinvention receives a spread signal to be received. The propagation pathestimating device according to the present invention includes receivingmeans, despreading means, propagation path estimating means, and controlmeans.

The receiving means receives a signal to be received that has a pilotsignal and a control signal specifying a demodulating method. Thedespreading means despreads the received signal, and then outputs thepilot signal and the control signal. The propagation path estimatingmeans obtains an amount of phase rotation of the received signal on thebasis of the pilot signal. The control means controls length of thepilot signal used by the propagation path estimating means on the basisof the control signal.

According to the invention comprised as described above, the controlmeans controls the length of the pilot signal used by the propagationpath estimating means on the basis of the control signal specifying thedemodulating method. Thereby the length of the pilot signal used by thepropagation path estimating means can be increased as appropriateaccording to the demodulating method, and a function (a function ofreducing the length of the pilot signal used) provided for ademodulating method that is most susceptible to deterioration inaccuracy may not be performed at all times.

Further, the present invention relates to a despreading device. Thedespreading device according to the present invention receives a spreadsignal to be received. The despreading device according to the presentinvention includes receiving means, despreading means, and controlmeans.

The receiving means receives a signal to be received that has a pilotsignal and a control signal specifying a demodulating method. Thedespreading means despreads the received signal, and then outputs thepilot signal and the control signal. The control means controls lengthof the pilot signal despread by the despreading means on the basis ofthe control signal.

According to the invention comprised as described above, the controlmeans controls the length of the pilot signal despread on the basis ofthe control signal specifying the demodulating method. Thereby thelength of the pilot signal despread can be increased as appropriateaccording to the demodulating method, and a function (a function ofreducing the length of the pilot signal despread) provided for ademodulating method that is most susceptible to deterioration inaccuracy may not be performed at all times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a comparison of modulating methods (QPSK,16-QAM, and 64QAM) and effects of shifts in reception timing.

FIG. 2 is a graph showing a comparison of modulating methods (QPSK,16-QAM, and 64QAM) and effects of errors in synchronous detection.

FIG. 3 is a block diagram showing a configuration of a base station inan adaptive modulation communication system.

FIGS. 4A, 4B, and 4C are diagrams showing symbol maps of the modulatingmethods (QPSK, 16-QAM, and 64-QAM), and show a symbol map of QPSK (FIG.4A), a symbol map of 16-QAM (FIG. 4B), and a symbol map of 64-QAM (FIG.4C).

FIG. 5 is a block diagram showing details of a configuration of anadaptive coding/modulating unit 1109.

FIG. 6 is a diagram showing contents of signals transmitted and receivedby the base station to and from a user terminal via a transmitting andreceiving device 1101.

FIG. 7 is a block diagram showing a configuration of a user terminal(receiving apparatus) according to an embodiment of the presentinvention.

FIG. 8 is a diagram showing an amount of phase rotation.

FIG. 9 is a diagram showing lengths of a pilot signal used in obtainingan average.

FIGS. 10A, 10B, and 10C are time charts when a cycle of a SYNC pulse fordata trigger timing is changed, and show a state of 64-QAM data transfer(FIG. 10A), a state of 16-QAM transfer (FIG. 10B), and a state of QPSKtransfer (FIG. 10C).

FIGS. 11A, 11B, and 11C are time charts when a data transfer clock speedis changed, and show a state of 64-QAM data transfer (FIG. 11A), a stateof 16-QAM transfer (FIG. 11B), and a state of QPSK transfer (FIG. 11C).

FIG. 12 is a flowchart illustrating operation of the embodiment of thepresent invention.

FIG. 13 is a flowchart illustrating operation of a modification of theembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Prior to description of an embodiment of the present invention, anadaptive modulation communication system on which the embodiment of thepresent invention is predicated will be described.

FIG. 3 is a block diagram showing a configuration of a base station inthe adaptive modulation communication system. The base station includesa transmitting and receiving device 1101, a despreading unit 1102, ademodulating unit 1103, a reception quality bit extracting unit 1104, acontrol unit 1105, a control data generating unit 1106, acoding/modulating unit 1107, a spreading unit 1108, an adaptivecoding/modulating unit 1109, and a D/A conversion unit 1110.

The transmitting and receiving device 1101 receives a reception qualitydata signal transmitted from a user terminal, which will be describedlate. The reception quality data signal indicates quality of a signalreceived by the user terminal from the base station. The receptionquality data signal is spread and modulated by the user terminal. Also,the transmitting and receiving device 1101 transmits a signal outputtedby the D/A conversion unit 1110 to the user terminal.

The despreading unit 1102 despreads and outputs the reception qualitydata signal. The demodulating unit 1103 demodulates and outputs theoutput of the despreading unit 1102. Thereby, the reception quality datasignal in a state before being spread and modulated is generated. Thereception quality bit extracting unit 1104 extracts from the receptionquality data signal information of the quality of the signal received bythe user terminal from the base station (referred to as receptionquality data).

According to the extracted reception quality data, the control unit 1105determines a coding method for coding and a modulating method formodulating communication data, a control signal, and a pilot signal tobe sent to the user terminal.

In this case, for simple description, the coding method and themodulating method are selected from four combinations shown in Table 2.

TABLE 2 Mode Coding method Modulating method 0 R = 1/2 QPSK 1 R = 1/216-QAM 2 R = 3/4 16-QAM 3 R = 3/4 64-QAM

Table 2 shows two coding methods represented by R=½ and R=¾. The codingmethod represented by R=½ adds one redundant bit to one bit of inputdata. The coding unit represented by R=¾ adds one redundant bit to threebits of input data.

Code of R=½ has a larger number of redundant bits, thus resulting in ahigh error correction capability, but reduces transmissiblecommunication data. On the other hand, the code error correctioncapability of R=¾ is lower than that of R=½, but transmissiblecommunication data is increased.

QPSK, 16-QAM, and 64-QAM is used as the modulating method. FIGS. 4A, 4B,and 4C show symbol maps of these modulating methods. As shown in FIG.4A, the QPSK modulation maps coded 2-bit data into one symbol. As shownin FIG. 4B, 16-QAM maps 4-bit data into one symbol. As shown in FIG. 4C,64-QAM maps 6-bit data into one symbol.

Referring to FIGS. 4A to 4C, when a transmissible symbol rate is fixed,an amount of transmissible data is maximum for 64 QAM, which maps themaximum number of bits into one symbol, and is minimum for QPSK. On theother hand, 64 QAM is easily affected by noise because of short distancebetween adjacent symbols, and QPSK has the most favorable errorcharacteristics at the same noise level.

Thus, a relation of the amounts of data transferred is expressed asfollows:(R=½, QPSK)<(R=½, 16-QAM)<(R=¾, 16-QAM)<(R=¾, 64QAM)

On the other hand, a relation of noise resisting characteristics isexpressed as follows:(R=½, QPSK)>(R=½, 16-QAM)>(R=¾, 16-QAM)>(R=¾, 64QAM)

In a case of a good propagation path with a low noise (a case of goodreception quality), the control unit 1105 selects a coding/modulatingcombination allowing transfer of a large amount of data. In a case of apoor propagation path with a high noise (a case of poor receptionquality), the control unit 1105 reduces the amount of data transferred,and selects a coding/modulating combination for improving noiseresisting characteristics.

The control data generating unit 1106 generates a control signal forcommunicating the coding/modulating method selected by the control unit1105 to the user terminal. The coding/modulating unit 1107 subjects anoutput of the control data generating unit 1106 to coding/modulatingprocessing by a predetermined method. The coding/modulating unit 1107generally performs QPSK modulation.

The spreading unit 1108 spreads a pilot signal, communication dataoutputted from the adaptive coding/modulating unit 1109, and the controlsignal outputted from the coding/modulating unit 1107 by using differentspreading codes.

The adaptive coding/modulating unit 1109 subjects communication data(for example packet data) to coding/modulating processing by the codingmethod and the modulating method selected by the control unit 1105. FIG.5 shows details of a configuration of the adaptive coding/modulatingunit 1109. The adaptive coding/modulating unit 1109 has switches 1601and 1604, coding units 1602 a to 1602 d, and modulating units 1603 a to1603 d. The switches 1601 and 1604 are operated to select either one ofa plurality of series circuits (1602 a-1603 a, 1602 b-1603 b, 1602c-1603 c, and 1602 d-1603 d) formed by the coding units 1602 a to 1602 don an input side and the modulating units 1603 a to 1603 d on an outputside according to the coding method and the modulating method selectedby the control unit 1105. The coding units 1602 a to 1602 d add errorcorrection code to a signal inputted thereto, that is, code the signalinputted thereto, and then output the coded signal. The modulating units1603 a to 1603 d subject the signal coded by the coding units 1602 a to1602 d to modulation symbol mapping, that is, modulate the signal, andthen output the modulated signal.

The D/A conversion unit 1110 converts a digital signal outputted by thespreading unit 1108 into an analog signal, and then outputs the analogsignal to the transmitting and receiving device 1101.

FIG. 6 shows contents of signals transmitted and received by the basestation to and from the user terminal via the transmitting and receivingdevice 1101. The transmitting and receiving device 1101 receives areception quality data signal 2 sent from the user terminal in an upcontrol channel, and transmits a control signal 4 to the user terminalin a down control channel. As described above, the control signal isdetermined on the basis of the reception quality data signal 2. Thetransmitting and receiving device 1101 further transmits communicationdata 6 to the user terminal in a down data channel immediately aftertransmitting the control signal.

An embodiment of the present invention relates to the user terminal. Theembodiment of the present invention will hereinafter be described withreference to drawings.

FIG. 7 is a block diagram showing a configuration of a user terminal(receiving apparatus) according to an embodiment of the presentinvention. The user terminal includes a transmitting and receivingdevice 101, an A/D conversion unit 111, a despreading unit 102, acontrol data demodulating and decoding unit 103, a control unit 104, adata demodulating and decoding unit 105, a propagation path estimatingunit 106, a reception quality estimating unit 107, a reception qualitybit inserting unit 108, a modulating unit 109, a spreading unit 110, asampling rate supplying unit 112, and an interference suppressing unit113.

The transmitting and receiving device 101 receives a signal transmittedfrom the base station (see FIG. 3). The signal received will be referredto as a received signal. The received signal has communication data, apilot signal, and a control signal, and is spread and modulated in thebase station. The control signal specifies a modulating method, that is,a demodulating method. For example, when the control signal indicatesthat the received signal is modulated by QPSK in the base station, thedemodulating method needs to be QPSK. That is, the control signalspecifies QPSK as the demodulating method. The control signal alsospecifies a decoding method. Also, the transmitting and receiving device101 transmits a reception quality data signal outputted by the spreadingunit 110 to the base station.

The A/D conversion unit 111 and the despreading unit 102 includedespreading means for despreading the received signal and thenoutputting communication data, a pilot signal, and a control signal.Alternatively, only the despreading unit 102 may be considered to be thedespreading means. In this case, the transmitting and receiving device101 and the A/D conversion unit 111 form receiving means. The A/Dconversion unit 111 converts the received signal into a digital signal.The despreading unit 102 despreads the digitized received signal, andthen outputs communication data, a pilot signal, and a control signal.

The interference suppressing unit 113 suppresses multipath interferencein an output of the A/D conversion unit 111. The suppression ofmultipath interference specific to a mobile communication environmentuses an interference canceller shown in Higuchi et al. “Characteristicsof Ultrahigh Speed Packet Transmission Using Multipath InterferenceCanceller in W-CDMA Downlink” (Technical Report of the Institute ofElectronics, Information and Communication Engineers, RCS2000-134,October 2000) or the like, and an equalizer shown in Hooli et al.“Multiple Access Interference Suppression with Linear Chip Equalizers inWCDMA Downlink Receivers”, Proc. Global Telecommunications Conf. Pp.467-471. November 1999 or the like. For example, the pilot signal outputof the despreading unit 102 is inputted to the interference suppressingunit 113, propagation path characteristics are estimated from a pilotcomponent, and then the propagation path characteristics are equalizedadaptively.

Processing by the interference suppressing unit 113 is performed at asampling rate. The processing therefore requires very high speedarithmetic processing and consumes much power. Hence, it is notdesirable for the interference suppressing unit 113 to suppressmultipath interference at all times. On the other hand, when themodulating method is 64-QAM or 16-QAM, susceptibility to multipathinterference is increased as compared with the modulating method ofQPSK. Thus, the control unit 104 reads the demodulating method, andsends the information to the interference suppressing unit 113. When thedemodulating method is 64-QAM or 16-QAM, the interference suppressingunit 113 suppresses multipath interference, and when the demodulatingmethod is QPSK, the interference suppressing unit 113 does not suppressmultipath interference.

The control data demodulating and decoding unit 103 demodulates anddecodes the control signal by a predetermined method. For example, whenQPSK modulation of the control signal is predetermined, the controlsignal is demodulated by the QPSK method.

The control unit 104 reads the specified demodulating method anddecoding method from the control signal outputted from the control datademodulating and decoding unit 103. On the basis of the specifieddemodulating method, the control unit 104 controls the A/D conversionunit 111, the despreading unit 102, the data demodulating and decodingunit 105, the propagation path estimating unit 106, the sampling ratesupplying unit 112, and the interference suppressing unit 113. Detailsof the control will be described in conjunction with description of thedata demodulating and decoding unit 105, the propagation path estimatingunit 106, and the sampling rate supplying unit 112. The control of theinterference suppressing unit 113 is as described above.

The data demodulating and decoding unit 105 demodulates and decodes thecommunication data outputted from the despreading unit 102. Thedemodulating method and the decoding method are specified in the controlsignal, and sent from the control unit 104.

The propagation path estimating unit 106 obtains an amount of phaserotation on the basis of the pilot signal outputted from the despreadingunit 102. As shown in FIG. 8, the amount of phase rotation is a phasedifference between the received signal and an expected received signal.The amount of phase rotation is obtained after averaging M pilotsymbols, in consideration of effects of a noise component added on apilot channel. The number of pilot symbols used, that is, length of thepilot signal used is determined on the basis of the demodulating methodspecified in the control signal. The demodulating method is sent fromthe control unit 104.

Since the amount of noise added to the pilot symbols varies depending onpropagation path characteristics, it is effective to change the lengthof the pilot signal (number of pilot symbols) according to thepropagation path characteristics. Specifically, when there is a largeamount of noise, it is desirable to increase the length of the pilotsignal used in obtaining an average and thereby reduce effects of thenoise. When there is a small amount of noise, it is desirable todecrease the length of the pilot signal used in obtaining an average andthereby obtain data (amount of phase rotation) in as short a time aspossible.

When there is a large amount of noise, the demodulating method specifiedin the control signal is QPSK. Thus, when the demodulating method sentfrom the control unit 104 is QPSK, the propagation path estimating unit106 increases the length of the pilot signal used in obtaining anaverage. When there is a small amount of noise, the demodulating methodspecified in the control signal is 64 QAM. Thus, when the demodulatingmethod sent from the control unit 104 is 64 QAM, the propagation pathestimating unit 106 decreases the length of the pilot signal used inobtaining an average. The thus set length of the pilot signal used inobtaining an average is shown in FIG. 9. The length of the pilot signalis shortest (six pilot symbols) in the demodulating method of 64 QAM,while the length of the pilot signal is longest (20 pilot symbols) inthe demodulating method of QPSK. The length of the pilot signal isintermediate (10 pilot symbols) in the demodulating method of 16-QAM.

The control of the length of the pilot signal has been describedsupposing that the control unit 104 controls the propagation pathestimating unit 106. However, the control unit 104 can also control thelength of the pilot signal despread by the despreading unit 102. Thelength of the pilot signal despread in 64 QAM is shortest, while thelength of the pilot signal despread in the demodulating method of QPSKis longest. The length of the pilot signal despread is intermediate inthe demodulating method of 16-QAM.

The reception quality estimating unit 107 estimates a signal-to-noiseratio of the down data channel. The signal-to-noise ratio to beestimated is calculated as follows, by obtaining a signal-to-noise ratioof a pilot channel symbol code-multiplexed and transmitted in parallelwith the down data channel, and taking into consideration a differencebetween pilot channel power and data channel power.

The reception quality bit inserting unit 108 inserts the estimatedreception quality value (Data_SNR) into a user terminal transmissionsignal to be transmitted to the base station by the user terminal, andthen outputs the result as a reception quality data signal. Themodulating unit 109 modulates and outputs the reception quality datasignal. The spreading unit 110 spreads the modulated reception qualitydata signal, and then outputs the spread reception quality data signalto the transmitting and receiving device 101.

The sampling rate supplying unit 112 supplies a sampling rate of thedespreading unit 102 and the A/D conversion unit 111. The sampling rateis determined on the basis of the demodulating method specified in thecontrol signal. The demodulating method is sent from the control unit104.

The A/D conversion unit 111 converts the analog received signal into adigital signal. For fine synchronous processing in a baseband unit, theA/D conversion is performed by oversampling over a spread chip rate. Inprocessing a wideband received signal such as of W-CDMA, whilehigh-speed A/D conversion is required, it is important, for reduction inpower consumption, to select the lowest oversampling rate that canmaintain reception characteristics. In W-CDMA using the QPSK modulation,four- or eight-times oversampling is generally appropriate. The 16-QAMmodulation requires a higher sampling rate. The 64-QAM modulationrequires a still higher sampling rate than the 16-QAM modulation.

Thus, when the demodulating method sent from the control unit 104 is theQPSK modulation, the sampling rate supplying unit 112 supplies asampling rate four times the chip rate. When the demodulating methodsent from the control unit 104 is the 16-QAM modulation, the samplingrate supplying unit 112 supplies a sampling rate eight times the chiprate. When the demodulating method sent from the control unit 104 is the64 QAM modulation, the sampling rate supplying unit 112 supplies asampling rate 16 times the chip rate.

Thus, the sampling rate supplying unit 112 supplies the sampling rate 16times the chip rate only in the case of the 64-QAM modulation. In thecases of the other modulating methods, the sampling rate supplying unit112 supplies the lower sampling rates.

The sampling rate supplying unit 112 can supply the sampling rate bychanging a cycle of a SYNC pulse for data trigger timing, as shown inFIGS. 10A, 10B, and 10C. FIG. 10A shows a state of 64 QAM data transfer;FIG. 10B shows a state of 16-QAM transfer; and FIG. 10C shows a state ofQPSK transfer.

In addition, as shown in FIGS. 11A, 11B, and 11C, the sampling ratesupplying unit 112 can supply the sampling rate by changing a datatransfer clock speed. FIG. 11A shows a state of 64 QAM data transfer;FIG. 11B shows a state of 16-QAM transfer; and FIG. 11C shows a state ofQPSK transfer.

Operation of the embodiment of the present invention will next bedescribed with reference to a flowchart of FIG. 12.

First the transmitting and receiving device 101 receives a controlsignal (S10). The received control signal is digitized by the A/Dconversion unit 111, despread by the despreading unit 102, anddemodulated and decoded by the control data demodulating and decodingunit 103. Incidentally, it is supposed that the control signal is set tobe subjected to the QPSK modulation in the base station. Thus, thesampling rate is set to be the minimum value, or four times the chiprate. Also, the demodulating method is the QPSK method. Further, thelength of a pilot signal (number of pilot symbols) used in obtaining anaverage or the length of the pilot signal despread is set to the maximumlength of 20 symbols.

The control unit 104 reads a specified demodulating method and decodingmethod from the control signal outputted from the control datademodulating and decoding unit 103 (S12). Then the control unit 104determines whether or not communication data is received (S14). When nocommunication data is received (S14, No), the processing returns to thereception of a control signal (S10). When communication data is received(S14, Yes), the control unit 104 determines the sampling rate of the A/Dconversion unit 111 and the like and the length of the pilot signal(number of pilot symbols) used in obtaining an average.

When the demodulating method specified in the control signal is QPSK(S16, Yes), the sampling rate and the length of the pilot signal used inobtaining an average (referred to as pilot averaging length) are notchanged. That is, the control unit 104 controls the sampling ratesupplying unit 112 to set the sampling rate to the minimum value, orfour times the chip rate. Also, the control unit 104 controls thepropagation path estimating unit 106 to set the pilot averaging lengthto the maximum length of 20 symbols. Incidentally, the control unit 104may control the despreading unit 102 to set the length (number of pilotsymbols) of the pilot signal despread to the maximum length of 20symbols. The control unit 104 controls the interference suppressing unit113 to leave suppression of multipath interference stopped.

The demodulating method of QPSK means that processing may be at lowspeed, and hence that the sampling rate may be low. Since it is expectedthat much noise is added, however, the pilot averaging length needs tobe increased to suppress the noise. Accordingly, the sampling rate isset to the minimum value, and the pilot averaging length is set to themaximum value. When the demodulating method is QPSK, susceptibility tomultipath interference is less, and therefore the multipath interferenceinterferes less with communications without being suppressed. Thus, themultipath interference is not suppressed, whereby power consumption isreduced.

When the demodulating method specified in the control signal is 16-QAM(S16, No, and S20, Yes), the control unit 104 controls the sampling ratesupplying unit 112 to set the sampling rate to the intermediate value ofeight times the chip rate (S22). Also, the control unit 104 controls thepropagation path estimating unit 106 to set the pilot averaging lengthto the intermediate length of 10 symbols (S24). Incidentally, thecontrol unit 104 may control the despreading unit 102 to set the length(number of pilot symbols) of the pilot signal despread to theintermediate length of 10 symbols. The control unit 104 then controlsthe interference suppressing unit 113 to suppress multipath interference(S26).

The demodulating method of 16-QAM means that processing is at mediumspeed, and hence that a medium sampling rate is required. Since it isexpected that a medium level of noise is added, on the other hand, it isdesirable that the pilot averaging length be set intermediate for boththe suppression of the noise and the instantaneous measurement of anamount of phase rotation. Accordingly, the sampling rate is set to theintermediate value, and the pilot averaging length is set to theintermediate value. When the demodulating method is 16-QAM,susceptibility to multipath interference is increased, and therefore themultipath interference is suppressed.

When the demodulating method specified in the control signal is 64 QAM(S16, No, and S20, No), the control unit 104 controls the sampling ratesupplying unit 112 to set the sampling rate to the maximum value of 16times the chip rate (S32). Also, the control unit 104 controls thepropagation path estimating unit 106 to set the pilot averaging lengthto the minimum length of six symbols (S34). Incidentally, the controlunit 104 may control the despreading unit 102 to set the length (numberof pilot symbols) of the pilot signal despread to the minimum length ofsix symbols. The control unit 104 then controls the interferencesuppressing unit 113 to suppress multipath interference (S36).

The demodulating method of 64 QAM means that processing is at highspeed, and hence that a high sampling rate is required. Since it isexpected that a low level of noise is added, on the other hand, it isdesirable that the pilot averaging length be reduced so that theinstantaneous measurement of an amount of phase rotation takesprecedence over the suppression of the noise. Accordingly, the samplingrate is set to the maximum value, and the pilot averaging length is setto the minimum value. When the demodulating method is 64 QAM,susceptibility to multipath interference is increased, and therefore themultipath interference is suppressed.

After the sampling rate and the pilot averaging length are set asdescribed above, the transmitting and receiving device 101 receivescommunication data (S40). The communication data is digitized by the A/Dconversion unit 111, and then despread by the despreading unit 102. Thedespread communication data is supplied to the data demodulating anddecoding unit 105 to be demodulated and decoded. The demodulating anddecoding method is specified by the control signal sent to the datademodulating and decoding unit 105. At this time, an amount of phaserotation estimated by the propagation path estimating unit 106 isincluded in the control signal and is used for phase correction.

The pilot signal is sent in conjunction with the communication data, andis sent to the propagation path estimating unit 106 and the receptionquality estimating unit 107 via the A/D conversion unit 111 and thedespreading unit 102. On the basis of the pilot signal, the receptionquality estimating unit 107 estimates reception quality. The estimatedreception quality value is inserted into a user terminal transmissionsignal by the reception quality bit inserting unit 108, and then thereception quality bit inserting unit 108 outputs a reception qualitydata signal. The reception quality data signal is modulated by themodulating unit 109, spread by the spreading unit 110, and thentransmitted to the base station by the transmitting and receiving device101.

When the reception of the communication data as described above iscompleted, the control unit 104 sets the sampling rate to four times thechip rate (S42) and sets the pilot averaging length to 20 symbols (S44).The control unit 104 then stop the suppressing of multipath interferenceby the interference suppressing unit 113 (S46). That is, the controlunit 104 initializes the sampling rate, the pilot averaging length, andthe state of operation of the interference suppressing unit 113. Then,the processing returns to the reception of a control signal (S10).Incidentally, the processing is ended at an arbitrary point in time byturning off power.

According to the embodiment of the present invention, the control unit104 controls the sampling rate of the despreading means (the A/Dconversion unit 111 and the despreading unit 102) on the basis of thecontrol signal specifying the demodulating method (QPSK, 16-QAM, or 64QAM). Thereby the sampling rate for the demodulating method of QPSK or16-QAM can be set lower as appropriate than for the demodulating methodof 64 QAM. For example, the sampling rate can be set equal to eighttimes the chip rate (16-QAM) or four times the chip rate (QPSK). Thus, afunction (setting the sampling rate equal to 16 times the chip rate)provided for the demodulating method (64 QAM) that is most susceptibleto deterioration in accuracy may not be performed at all times.

Also, the control unit 104 controls the length (pilot averaging length)of the pilot signal used by the propagation path estimating unit 106 onthe basis of the control signal specifying the demodulating method(QPSK, 16-QAM, or 64 QAM). Thereby the length of the pilot signal usedby the propagation path estimating unit 106 can be increased asappropriate according to the demodulating method. For example, the pilotaveraging length can be set to 10 symbols (16-QAM) or 20 symbols (QPSK).Thus, a function (setting the pilot averaging length to six symbols)provided for the demodulating method (64 QAM) that is most susceptibleto deterioration in accuracy may not be performed at all times.

Further, the control unit 104 controls the length of the despread pilotsignal on the basis of the control signal specifying the demodulatingmethod (QPSK, 16-QAM, or 64 QAM). Thereby the length of the despreadpilot signal can be increased as appropriate according to thedemodulating method. For example, the length of the despread pilotsignal can be set to 10 symbols (16-QAM) or 20 symbols (QPSK). Thus, afunction (setting the length of the despread pilot signal to sixsymbols) provided for the demodulating method (64 QAM) that is mostsusceptible to deterioration in accuracy may not be performed at alltimes.

Further, the control unit 104 controls the state of operation of theinterference suppressing unit 113 on the basis of the control signalspecifying the demodulating method (QPSK, 16-QAM, or 64 QAM). Therebythe suppression of multipath interference can be controlled according tothe demodulating method. For example, the suppression of multipathinterference can be controlled to be performed (16-QAM and 64 QAM) ornot to be performed (QPSK). Thus, a function (performing the suppressionof multipath interference) provided for the demodulating method (16-QAMand 64 QAM) that is most susceptible to deterioration in accuracy maynot be performed at all times.

It is to be noted that in the present embodiment, the sampling rate, thepilot averaging length, and the state of operation of the interferencesuppressing unit 113 are determined on the basis of the modulatingmethod (demodulating method) read from the control signal; however, thesampling rate and the like may be determined according to a type ofreceived signal, that is, according to whether there is only a controlsignal or whether there is also communication data. This providessimilar effects. Operation in this case will be described with referenceto a flowchart of FIG. 13.

The reception of a control signal (S10) and the reading of thedemodulating method (S12) are the same as in FIG. 12. Then the controlunit 104 determines whether or not communication data is received (S14).When no communication data is received (S14, No), the sampling rate andlength of a pilot signal used in obtaining an average (referred to aspilot averaging length) are not changed. When communication data isreceived (S14, Yes) the control unit 104 controls the sampling ratesupplying unit 112 to set the sampling rate to the maximum value of 16times the chip rate (S32). Also, the control unit 104 controls thepropagation path estimating unit 106 to set the pilot averaging lengthto the minimum length of six symbols (S34). Incidentally, the controlunit 104 may control the despreading unit 102 to set the length (numberof pilot symbols) of the pilot signal despread to the minimum length ofsix symbols. The control unit 104 then controls the interferencesuppressing unit 113 to suppress multipath interference.

The reception of communication data (S40) and processing thereafter arethe same as in FIG. 12.

The embodiment described above can be realized as follows. A computerincluding a CPU, a hard disk, a flash memory, and a media (such asfloppy disks, CD-ROMs, memory sticks and the like) reading device makesthe media reading device read a medium on which a program for realizingthe above-described parts is recorded and then installs the program onthe hard disk, in the flash memory or the like. The above-describedfunctions can be realized also by such a method.

A preferred embodiment of the present invention has been describedabove. However, the present invention is susceptible of various changes.

1. A despreading device receiving a spread signal to be received, saiddespreading device comprising: receiving means for receiving said signalto be received that has communication data and a control signalspecifying a demodulating method; despreading means for despreading thereceived signal on the basis of a sampling rate and then outputting saidcontrol signal and the communication data; sampling rate supplying meansfor supplying said sampling rate to said despreading means; datademodulating means for demodulating the communication data; controlmeans for controlling said sampling rate and a demodulating method ofthe demodulating means on the basis of said control signal; and outputmeans for outputting the sampling rate.
 2. A propagation path estimatingdevice receiving a spread signal to be received, said propagation pathestimating device comprising: receiving means for receiving said signalto be received that has communication data, a pilot signal and a controlsignal specifying a demodulating method; despreading means fordespreading the received signal, and then outputting said pilot signaland said control signal and the communication data; propagation pathestimating means for obtaining an amount of phase rotation of saidreceived signal on the basis of said pilot signal; data demodulatingmeans for demodulating the communication data; control means forcontrolling a demodulating method of the demodulating means and a lengthof said pilot signal used by said propagation path estimating means onthe basis of said control signal; and output means for outputting thepilot signal.
 3. A despreading device receiving a spread signal to bereceived, said despreading device comprising: receiving means forreceiving said signal to be received that has communication data, apilot signal and a control signal specifying a demodulating method;despreading means for despreading the received signal, and thenoutputting the communication data, said pilot signal and said controlsignal; control means for controlling a demodulating method of thedemodulating means and a length of said pilot signal despread by saiddespreading means on the basis of said control signal; and output meansfor outputting the pilot signal.
 4. A receiving apparatus for receivinga spread signal to be received, said receiving apparatus comprising:receiving means for receiving said signal to be received that hascommunication data and a control signal specifying a demodulatingmethod; despreading means for despreading the received signal on thebasis of a sampling rate, and then outputting said communication dataand said control signal; sampling rate supplying means for supplyingsaid sampling rate to said despreading means; data demodulating meansfor demodulating said communication data; control means for controllingsaid sampling rate and a demodulating method of said data demodulatingmeans on the basis of said control signal; and output means foroutputting the sampling rate.
 5. A receiving apparatus for receiving aspread signal to be received, said receiving apparatus comprising:receiving means for receiving said signal to be received that hascommunication data, a pilot signal, and a control signal specifying ademodulating method; despreading means for despreading the receivedsignal, and then outputting said communication data, said pilot signal,and said control signal; propagation path estimating means for obtainingan amount of phase rotation of said received signal on the basis of saidpilot signal; data demodulating means for demodulating saidcommunication data on the basis of said amount of phase rotation;control means for controlling length of said pilot signal used by saidpropagation path estimating means and a demodulating method of said datademodulating means on the basis of said control signal; and output meansfor outputting the pilot signal.
 6. A receiving apparatus for receivinga spread signal to be received, said receiving apparatus comprising:receiving means for receiving said signal to be received that hascommunication data, a pilot signal, and a control signal specifying ademodulating method; despreading means for despreading the receivedsignal, and then outputting said communication data, said pilot signal,and said control signal; data demodulating means for demodulating saidcommunication data; control means for controlling length of said pilotsignal despread by said despreading means and a demodulating method ofsaid data demodulating means on the basis of said control signal; andoutput means for outputting the pilot signal.